X-ray imaging detectors that operate in a wide range of energies are useful in a large number of applications. High energy x-rays are used for x-ray imaging in radiation therapy treatments, and for security cargo inspections. In these applications, linac-generated MeV x-rays are used. In the keV x-ray range, x-ray detectors are used for medical x-ray CT imaging, security imaging, and non-destructive testing, by way of example.
In all of these applications, and in particular for high energy applications, it is desirable to increase the DQE (detective quantum efficiency) of the x-ray detectors. The DQE can be understood as the ratio of the amount of information contained in the incident x-ray flux to the amount of information in the output signal. The later is always reduced due to the imperfections of the detector, including electronic noise, nonuniformity of the output, nonlinearity, etc.
A modern x-ray computed tomography detector is usually composed of a pixilated scintillator array to convert x-ray energy into light, and a photosensor, such as a semiconductor photodiode array, to convert the light into an electrical signal. Similar detector arrays can be used in radiation treatment imaging for the tumor localization and dose verification, as well as in security x-ray imaging applications.
These x-ray detectors typically include in their output signals parasitic contributions from electron-hole pairs created by direct conversion of x-rays that penetrate the scintillator without interacting with the scintillator material. Such direct conversion of x-rays into electric charge carriers in the photodiode result in output signal contributions that negatively affect the DQE of the x-ray detectors.
Accordingly, it is desirable to provide an x-ray detector having an improved DQE, by substantially reducing such parasitic contributions to the detector output signal.